Multimetallic catalytic composite

ABSTRACT

Dehydrogenatable hydrocarbons are dehydrogenated by contacting them, at dehydrogenation conditions, with a multimetallic catalytic composite comprising a combination of catalytically effective amounts of a platinum group component, a cobalt component, and a bismuth component with a porous carrier material. A specific example of the nonacidic multimetallic catalytic composite disclosed herein is a combination of a platinum group component, a cobalt component, a bismuth component, and an alkali or alkaline earth component with a porous carrier material in amounts sufficient to result in a composite containing about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt, about 0.01 to about 5 wt. % bismuth and about 0.1 to about 5 wt. % alkali metal or alkaline earth metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of my prior, copending application Ser.No. 718,310 filed Aug. 27, 1976, now U.S. Pat. No. 4,079,097, Mar. 14,1978; which in turn is a continuation-in-part of my prior applicationSer. No. 602,935 filed Aug. 8, 1975 and issued Sept. 21, 1976 as U.S.Pat. No. 3,981,795. All of the teachings of these prior applications arespecifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method ofdehydrogenating a dehydrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a method ofdehydrogenating normal paraffin hydrocarbons containing 4 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another aspect, the presentinvention relates to a novel nonacidic multimetallic catalytic compositecomprising a combination of catalytically effective amounts of aplatinum group component, a cobalt component, a bismuth component, andan alkali or alkaline earth component with a porous carrier material.This nonacidic composite has highly beneficial characteristics ofactivity, selectivity, and stability when it is employed in thedehydrogenation of dehydrogenatable hydrocarbons such as aliphatichydrocarbons, naphthene hydrocarbons, and alkylaromatic hydrocarbons.

The conception of the present information followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity, and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior application, I disclosed a significantfinding with respect to a multimetallic catalytic composite meetingthese requirements. More specifically, I determined that a combinationof cobalt and bismuth can be utilized, under certain specifiedconditions, to beneficially interact with the platinum group componentof a dual-function catalyst with a resulting marked improvement in theperformance of such a catalyst. Now I have ascertained that a catalyticcomposite, comprising a combination of catalytically effective amountsof a platinum group component, a cobalt component, and a bismuthcomponent with a porous carrier material can have superior activity,selectivity and stability characteristics when it is employed in ahydrocarbon dehydrogenation process if these components are uniformlydispersed in the porous carrier material in the amounts specifiedhereinafter and if the oxidation state of the metallic ingredients arecarefully controlled so that substantially all of the platinum groupcomponent is present in the elemental metallic state, substantially allof the bismuth component is preferably present in a positive oxidationstate, and substantially all of the catalytically available cobaltcomponent is present in the elemental metallic state or in a state whichis reducible to the elemental metallic state under dehydrogenationconditions or in a mixture of these states. I have discerned, moreover,that a particularly preferred multimetallic catalytic composite of thistype contains not only a platinum group component, a cobalt component,and a bismuth component, but also an alkali or alkaline earth componentin an amount sufficient to ensure that the resulting catalyst isnonacidic.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasolines, perfumes, drying oils,ionexchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 4 to 30 carbon atoms per molecule. These normalmono-olefins can, in turn, be utilized in the synthesis of a vast numberof other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where they are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as the alkylaryl sulfonatetypes of detergents which are most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkylphenol base is prepared by thealkylation of phenol with these normal mono-olefins. Still another typeof detergents produced from these normal mono-olefins are thebiodegradable alkylsulfonates formed by the direct sulfation of thenormal mono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkylsulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in the petroleum,petrochemical, pharmaceutical, detergent, plastic, and the likeindustries. For example, ethylbenzene is dehydrogenated to producestyrene which is utilized in the manufacture of polystyrene plastics,styrene-butadiene rubber, and the like products. Isopropylbenzene isdehydrogenated to form alpha-methylstyrene which, in turn, isextensively used in polymer formation and in the manufacture of dryingoils, ion-exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability to perform its intended function with minimum interference ofside reactions for extended periods of time. The analytical terms usedin the art to broadly measure how well a particular catalyst performsits intended functions in a particular hydrocarbon conversion reactionare activity, selectivity, and stability, and for purposes of discussionhere, there terms are generally defined for a given reactant as follows:(1) activity is a measure of the catalyst's ability to convert thehydrocarbon reactant into products at a specified severity level whereseverity level means the specific reaction conditions used -- that is,the temperature, pressure, contact time, and presence of diluents suchas H₂ ; (2) selectivity usually refers to the amount of desired productor products obtained relative to the amount of the reactant charged orconverted; (3) stability refers to the rate of change with time of theactivity and selectivity parameters -- obviously the smaller rateimplying the more stable catalyst. In a dehydrogenation process, morespecifically, activity commonly refers to the amount of conversion thattakes place for a given dehydrogenatable hydrocarbon at a specifiedseverity level and is typically measured on the basis of disappearanceof the dehydrogenatable hydrocarbon; selectivity is typically measuredby the amount, calculated on a mole or weight percent of converteddehydrogenatable hydrocarbon basis, of the desired dehydrogenatedhydrocarbon obtained at the particular activity or severity level; andstability is typically equated to the rate of change with time ofactivity as measured by disappearance of the dehydrogenatablehydrocarbon and of selectivity as measured by the amount of desireddehydrogenated hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found a multimetallic catalytic composite which possessesimproved activity, selectivity, and stability when it is employed in aprocess for the dehydrogenation of dehydrogenatable hydrocarbons. Inparticular, I have determined that the use of a multimetallic catalyst,comprising a combination of catalytically effective amounts of aplatinum group component, a cobalt component, and a bismuth componentwith a porous refractory carrier material, can enable the performance ofa hydrocarbon dehydrogenation process to be substantially improved ifthe metallic components are uniformly dispersed throughout the carriermaterial in the amounts specified hereinafter and if their oxidationstates are carefully controlled to be in the states hereinafterspecified. Moreover, particularly good results are obtained when thiscomposite is combined with an amount of an alkali or alkaline earthcomponent sufficient to ensure that the resulting catalyst is nonacidicand utilized to produce dehydrogenated hydrocarbons containing the samecarbon structure as the reactant hydrocarbon but fewer hydrogen atoms.This nonacidic composite is particularly useful in the dehydrogenationof long chain normal paraffins to produce the corresponding normalmono-olefin with minimization of side reactions such as skeletalisomerization, aromatization, cracking and polyolefin formation. In sum,the present invention involves the significant finding that acombination of a cobalt component and a bismuth component can beutilized under the circumstances specified herein to beneficiallyinteract with and promote a dehydrogenation catalyst containing aplatinum group metal.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing a multimetallic catalytic composite comprising catalyticallyeffective amounts of a platinum group component, a cobalt component, anda bismuth component combined with a porous carrier material. A secondobject is to provide a novel nonacidic catalytic composite havingsuperior performance characteristics when utilized in a dehydrogenationprocess. Another object is to provide an improved method for thedehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins which method minimizes undesirable side reactions such ascracking, skeletal isomerization, polyolefin formation,disproportionation and aromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon whichcomprises contacting the hydrocarbon at dehydrogenation conditions witha multimetallic catalytic composite comprising a porous carrier materialcontaining a uniform dispersion of catalytically effective and availableamounts of a platinum group component, a cobalt component, and a bismuthcomponent. Substantially all of the platinum group component is,moreover, present in the composite in the elemental metallic state, andsubstantially all of the catalytically available cobalt component ispresent in the corresponding elemental metallic state and/or in a statewhich is reducible to the corresponding elemental metallic state underdehydrogenation conditions. Further, these components are present inthis composite in amounts, calculated on an elemental basis, sufficientto result in the composite containing about 0.01 to about 2 wt. %platinum group metal, about 0.05 to about 5 wt. % cobalt, and about 0.01to about 5 wt. % bismuth.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic compound containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends a nonacidic catalytic compositecomprising a porous carrier material having uniformly dispersed thereincatalytically effective and available amounts of a platinum groupcomponent, a cobalt component, a bismuth component, and an alkali oralkaline earth component. These components are preferably present inamounts sufficient to result in the catalytic composite containing, onan elemental basis, about 0.01 to about 2 wt. % platinum group metal,about 0.1 to about 5 wt. % of the alkali metal or alkaline earth metal,about 0.05 to about 5 wt. % cobalt, and about 0.01 to about 5 wt. %bismuth. In addition, substantially all of the platinum group componentis present in the elemental metallic state, substantially all of thebismuth component is preferably present in a positive oxidation state,substantially all of the catalytically available cobalt component ispresent in the elemental metallic state and/or in a state which isreducible to the elemental metallic state under dehydrogenationconditions and substantially all of the alkali or alkaline earthcomponent is present in an oxidation state above that of the elementalmetal.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon which comprises contacting the hydrocarbonwith the nonacidic catalytic composite described in the third embodimentat dehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. There are hereinafter given in the following detaileddiscussion of each of these facets of the present invention. It is to beunderstood that (1) the term "nonacidic" means that the catalystproduces less than 10% conversion of 1-butene to isobutylene when testedat dehydrogenation conditions and, preferably, less than 1% and (2) theexpression "uniformly dispersed throughout a carrier material" isintended to mean that the amount of the subject component, expressed ona weight percent basis, is approximately the same in any reasonablydivisible portion of the carrier material as it is in gross.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast one pair of adjacent carbon atoms having hydrogen attachedthereto. That is, it is intended to include within the scope of thepresent invention, the dehydrogenation of any organic compound capableof being dehydrogenated to produce products containing the same numberof carbon atoms but fewer hydrogen atoms, and capable of being vaporizedat the dehydrogenation temperatures used herein. More particularly,suitable dehydrogenatable hydrocarbons are: aliphatic compoundscontaining 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbonswhere the alkyl group contains 2 to 6 carbon atoms, and naphthenes oralkyl-substituted naphthenes. Specific examples of suitabledehydrogenatable hydrocarbons are: (1) alkanes such as ethanes, propane,n-butane, isobutane, n-pentane, isopentane, n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,2,2,3-trimethylbutane, and the like compounds; (2) naphthenes such ascyclopentane, cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 4 to 30 carbon atoms per molecule. Forexample, normal paraffin hydrocarbons containing about 10 to 18 carbonatoms per molecule are dehydrogenated by the subject method to producethe corresponding normal mono-olefin which can, in turn, be alkylatedwith benzene and sulfonated to make alkylbenzene sulfonate detergentshaving superior biodegradability. Likewise, n-alkanes having 10 to 18carbon atoms per molecule can be dehydrogenated to the correspondingnormal mono-olefin which, in turn, can be sulfonated or sulfated to makeexcellent detergents. Similarly, n-alkanes having 6 to 10 carbon atomscan be dehydrogenated to form the corresponding mono-olefin which can,in turn, be hydrated to produce valuable alcohols. Preferred feedstreams for the manufacture of detergent intermediates contain a mixtureof 4 or 5 adjacent normal paraffin homologues such as C₁₀ to C₁₃, C₁₁ toC₁₄, C₁₁ to C₁₅ and the like mixtures.

The multimetallic catalyst used in the present invention comprises aporous carrier material or support having combined therewith a uniformdispersion of catalytically effective amounts of a platinum groupcomponent, a cobalt component, a bismuth component, and, in thepreferred case, an alkali or alkaline earth component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high-surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the dehydrogenation process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts, such as: (1) activated carbon, coke,charcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated, for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, zinc oxide, magnesia, thoria, boria,silica-alumina, silica-magnesia, chromia-alumina, aluminaboria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, MnAl.sub. 2 O₄, CaAl₂ O₄ and other like compounds havingthe formula MO.Al₂ O₃ where M is a metal having a valence of 2; and (7)combinations of elements from one or more of these groups. The preferredporous carrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas the gamma-, eta-, and theta-alumina, with gamma- or eta-aluminagiving best results. In addition, in some embodiments the aluminacarrier material may contain minor proportions of other well-knownrefractory inorganic oxides such as silica, zirconia, magnesia, etc.;however, the preferred support is substantially pure gamma- oreta-alumina. Preferred carrier materials have an apparent bulk densityof about 0.2 to about 0.7 g/cc and surface area characteristics suchthat the average pore diameter is about 20 to about 30 Angstroms, thepore volume is about 0.1 to about 1 cc/g and the surface area is about100 to about 500 m² /g. In general, best results are typically obtainedwith a gamma-alumina carrier material which is used in the form ofspherical particles having: a relatively small diameter (i.e. typicallyabout 1/16 inch), an apparent bulk density of about 0.2 to about 0.6(most preferably about 0.3) g/cc, a pore volume of about 0.4 cc/g, and asurface area of about 150 to about 250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, etc., and utilized in any desiredsize. For the purpose of the present invention, a particularly preferredform of alumina is the sphere; and alumina spheres may be continuouslymanufactured by the well-known oil drop method which comprises: formingan alumina hydrosol by any of the techniques taught in the art andpreferably by reacting aluminum metal with hydrochloric acid, combiningthe resulting hydrosol with a suitable gelling agent and dropping theresultant mixture into an oil bath maintained at elevated temperatures.The droplets of the mixture remain in the oil bath until they set andform hydrogel spheres. The spheres are then continuously withdrawn fromthe oil bath and typically subjected to specific aging treatments in oiland an ammoniacal solution to further improve their physicalcharacteristics. The resulting aged and gelled particles are then washedand dried at a relatively low temperature of about 300° F. to about 400°F. and subjected to a calcination procedure at a temperature of about850° F. to about 1300° F. for a period of about 1 to about 20 hours. Itis a good practice to subject the calcined particles to a hightemperature treatment with steam in order to remove undesired acidiccomponents such as residual chloride. This procedure effects conversionof the alumina hydrogel to the corresponding crystalline gamma-alumina.See the teachings of U.S. Pat. No. 2,620,314 for additional details.

The expression "catalytically available cobalt" as used herein isintended to mean the portion of the cobalt component that is availablefor use in accelerating the dehydrogenation reaction of interest. Forcertain types of carrier materials which can be used in the preparationof the instant catalyst composite, it has been observed that a portionof the cobalt incorporated therein is essentially bound-up in thecrystal structure thereof in a manner which essentially makes itcatalytically unavailable; in fact it is more a part of the refractorycarrier material than a catalytically active component. Specificexamples of this effect are observed when the carrier material can forma spinel or spinel-like structure with a portion of the cobalt componentand/or when a refractory cobalt oxide or aluminate is formed by reactionof the carrier material (or precursor thereof) with a portion of thecobalt component. When this effect occurs, it is only with greatdifficulty that the portion of the cobalt bound-up with the support canbe reduced to a catalytically active state and the conditions requiredto do this are beyond the severity levels normally associated withdehydrogenation conditions and are in fact likely to seriously damagethe necessary porous characteristics of the support. In the cases wherecobalt can interact with the crystal structure of the support to rendera portion thereof catalytically unavailable, the concept of the presentinvention merely requires that the amount of cobalt added to the subjectcatalyst be adjusted to satisfy the requirements of the support as wellas the catalytically available cobalt requirements of the presentinvention. Against this background then, the hereinafter statedspecifications for oxidation state, particle size and dispersion of thecobalt component are to be interpreted as directed to a description ofthe catalytically available cobalt. On the other hand, thespecifications for the amount of cobalt used are to be interpreted toinclude all of the cobalt contained in the catalyst in any form.

One essential constituent of the multimetallic catalyst used in thepresent invention is a bismuth component. This component may in generalbe present in the instant catalytic composite in any catalyticallyactive form such as the elemental metal, a compound like the oxide,hydroxide, halide, oxyhalide, aluminate, or in chemical combination withone or more of the other ingredients of the catalyst. Although it is notintended to restrict the present invention by this explanation, it isbelieved that best results are obtained when the bismuth component ispresent in the composite in a form wherein substantially all of thebismuth moiety is in an oxidation state above that of the elementalmetal such as in the form of bismuth oxide or bismuth aluminate or amixture thereof and the subsequently described oxidation and reductionsteps that are preferably used in the preparation of the instantcatalytic composite are specifically designed to achieve this end. Theterm "bismuth aluminate" as used herein means a coordinated complex ofbismuth, oxygen, and aluminum which are not necessarily present in thesame fixed relationship for all cases covered herein. This bismuthcomponent can be used in any amount which is catalytically effective,with good results, obtained, on an elemental basis, with about 0.01 toabout 5 wt. % bismuth in the catalyst. Best results are ordinarilyachieved with about 0.05 to about 1 wt. % bismuth, calculated on anelemental basis.

This bismuth component may be incorporated in the catalytic composite inany suitable manner known to the art to result in a relatively uniformdispersion of the bismuth moiety in the carrier material, such as bycoprecipitation or cogelation with the porous carrier material, ionexchange with the gelled carrier material, or impregnation with thecarrier material either after, before, or during the period when it isdried and calcined. It is to be noted that it is intended to includewithin the scope of the present invention all conventional methods forincorporating and simultaneously uniformly distributing a metalliccomponent in a catalytic composite and the particular method ofincorporation used is not deemed to be an essential feature of thepresent invention. One preferred method of incorporating the bismuthcomponent into the catalytic composite involves cogelling orcoprecipitating the bismuth component in the form of the correspondinghydrous oxide during the preparation of the preferred carrier material,alumina. This method typically involves the addition of a suitablesol-soluble bismuth compound such as bismuth trichloride, bismuthoxynitrate, and the like to the alumina hydrosol and then combining thehydrosol with a suitable gelling agent and dropping the resultingmixture into an oil bath, etc., as explained in detail hereinbefore.Alternatively, the bismuth compound can be added to the gelling agent.After drying and calcining the resulting bismuth-containing gelledcarrier material in air, there is obtained an intimate combination ofalumina and bismuth oxide and/or bismuth aluminate. Another method ofincorporating the bismuth component into the catalytic compositeinvolves utilization of a soluble, decomposable compound or complex ofbismuth to impregnate the porous carrier material. In general, thesolvent used in this impregnation step is selected on the basis of thecapability to dissolve the desired bismuth compound without adverselyaffecting the carrier material and may be a suitable alcohol, ether,acid, and the like solvent, although it is preferably an aqueous, acidicsolution. Thus, the bismuth component may be added to the carriermaterial by commingling the latter with an aqueous acidic solution ofsuitable bismuth salt or complex of bismuth such as bismuth citrate,bismuth iodide, bismuth lactate, bismuth chloride, bismuth hydroxide,bismuth nitrate, bismuth oxynitrate, bismuth oxalate, bismuthsesquioxide, bismuth oxybromide, bismuth oxychloride, bismuthic acid,bismuth oxycarbonate, bismuth acetate, bismuth benzoate, bismuthbromide, bismuth tartrate, bismuth potassium tartrate, bismuth sodiumtartrate, bismuth ammonium citrate, and the like compounds. Aparticularly preferred impregnation solution comprises an acidicsolution of bismuth trichloride or nitrate or oxynitrate in water.Suitable acids for use in the impregnation solution are: inorganic acidssuch as hydrochloric acid, nitric acid, and the like, and stronglyacidic organic acids such as oxalic acid, malonic acid, citric acid, andthe like. In general, the bismuth component can be impregnated eitherprior to, simultaneously with, or after the other ingredients are addedto the carrier material. However, good results are obtained when thebismuth component is impregnated simultaneously with the platinum groupcomponent. In fact, a preferred preparation procedure involves a doubleimpregnation of the carrier material wherein the first impregnationsolution is an aqueous acidic solution of chloroplatinic acid, nitricacid and bismuth nitrate or oxynitrate.

A second essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as asecond component of the present composite. It is an essential feature ofthe present invention that substantially all of this platinum groupcomponent exists within the final catalytic composite in the elementalmetallic state. Generally, the amount of this component present in thefinal catalytic composite is small compared to the quantities of theother components combined therewith. In fact, the platinum groupcomponent generally will comprise about 0.01 to about 2 wt. % of thefinal catalytic composite, calculated on an elemental basis. Excellentresults are obtained when the catalyst contains about 0.05 to about 1wt. % of platinum, iridium, rhodium, or palladium metal. Particularlypreferred mixtures of these metals are platinum and iridium and platinumand rhodium.

This platinum group component may be incorporated in the catalyticcomposite in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium dioxide, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium chloroiridate, potassium rhodiumoxalate, etc. The utilization of a platinum, iridium, rhodium, orpalladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is ordinarilypreferred. Hydrogen chloride, nitric acid, or the like acid is alsogenerally added to the impregnation solution in order to furtherfacilitate the uniform distribution of the metallic componentsthroughout the carrier material. In addition, it is generally preferredto impregnate the carrier material after it has been calcined in orderto minimize the risk of washing away the valuable platinum or palladiumcompounds; however, in some cases it may be advantageous to impregnatethe carrier material when it is in a gelled state.

A third essential ingredient of the instant multimetallic catalyticcomposite is a cobalt component. Although this component may beinitially incorporated into the composite in many different decomposableforms which are hereinafter stated, my basic finding is that thecatalytically active state for hydrocarbon conversion with thiscomponent is the elemental metallic state. Consequently, it is a featureof this invention that substantially all of the catalytically availablecobalt component exists in the catalytic composite either in theelemental metallic state or in a state which is reducible to theelemental state under dehydrogenation conditions or in a mixture ofthese states. Examples of this last state are obtained when thecatalytically available cobalt component is initially present in theform of cobalt oxide, hydroxide, halide, oxyhalide, and the likereducible compounds. As a corollary to this basic finding on the activestate of the catalytically available cobalt component, it follows thatthe presence of the catalytically available cobalt in forms which arenot reducible at dehydrogenation conditions is to be scrupulouslyavoided if the full benefits of the present invention are to berealized. Illustrative of these undesired forms are cobalt sulfide andthe cobalt oxysulfur compounds such as cobalt sulfate. Best results areobtained when the composite initially contains all of the catalyticallyavailable cobalt component in the elemental metallic state or in areducible oxide state or in a mixture of these states. All availableevidence indicates that the preferred preparation procedure specificallydescribed in Example I results in a catalyst having the catalyticallyavailable cobalt component present in the form of a mixture of thereducible oxide and the elemental metal. Based on the performance ofsuch a catalyst, it is believed that substantially all of this reducibleoxide form of the cobalt component is reduced to the elemental metallicstate when a dehydrogenation process using this catalyst is started-upand lined-out at hydrocarbon dehydrogenation conditions. The cobaltcomponent may be utilized in the composite in any amount which iscatalytically effective, with the preferred amount being about 0.05 toabout 5 wt. % thereof, calculated on an elemental cobalt basis.Typically, best results are obtained with about 0.1 to about 2.5 wt. %cobalt. It is, additionally, preferred to select the specific amount ofcobalt from within this broad weight range as a function of the amountof the platinum group component, on an atomic basis, as is explainedhereinafter.

The cobalt component may be incorporated into the catalytic composite inany suitable manner known to those skilled in the catalyst formulationart to result in a relatively uniform distribution of the catalyticallyavailable cobalt in the carrier material such as coprecipitation,cogelation, ion-exchange, impregnation, etc. In addition, it may beadded at any stage of the preparation of the composite -- either duringpreparation of the carrier material or thereafter -- since the precisemethod of incorporation used is not deemed to be critical. However, bestresults are obtained when the catalytically available cobalt componentis relatively uniformly distributed throughout the carrier material in arelatively small particle or crystallite size having a maximum dimensionof less than 100 Angstroms, and the preferred procedures are the onesthat are known to result in a composite having a relatively uniformdistribution of the catalytically available cobalt moiety in arelatively small particle size. One acceptable procedure forincorporating this component into the composite involves cogelling orcoprecipitating the cobalt component during the preparation of thepreferred carrier material, alumina. This procedure usually comprehendsthe addition of a soluble, decomposable, and reducible compound ofcobalt such as cobalt acetate or chloride or nitrate to the aluminahydrosol before it is gelled. Alternatively, the reducible compound ofcobalt can be added to the gelling agent before it is added to thehydrosol. The resulting mixture is then finished by conventionalgelling, aging, drying, and calcination steps as explained hereinbefore.One preferred way of incorporating this component is an impregnationstep wherein the porous carrier material is impregnated with a suitablecobalt-containing solution either before, during, or after the carriermaterial is calcined or oxidized. The solvent used to form theimpregnation solution may be water, alcohol, ether, or any othersuitable organic or inorganic solvent provided the solvent does notadversely interact with any of the other ingredients of the composite orinterfere with the distribution and reduction of the cobalt component.Preferred impregnation solutions are aqueous solutions of water-soluble,decomposable, and reducible cobalt compounds such as cobaltous acetate,cobaltous benzoate, cobaltous bromate, cobaltous bromide, cobaltouschlorate and perchlorate, cobaltous chloride, cobaltic chloride,cobaltous fluoride, cobaltous iodide, cobaltous nitrate, hexamminecobalt(III) chloride, hexamminecobalt (III) nitrate, triethylenediamminecobalt(III) chloride, cobaltous hexamethylenetetramine, and the likecompounds. Best results are ordinarily obtained when the impregnationsolution is an aqueous solution of cobalt acetate or cobalt nitrate.This cobalt component can be added to the carrier material, either priorto, simultaneously with, or after the other metallic components arecombined therewith. Best results are usually achieved when thiscomponent is added after the platinum group and bismuth components havebeen impregnated via an aqueous impregnation solution. In fact,excellent results are obtained, as reported in the examples, with a twostep impregnation procedure using a second aqueous acidic impregnationsolution containing cobalt acetate or nitrate and nitric acid.

A highly preferred ingredient of the catalyst used in the presentinvention is the alkali or alkaline earth component. More specifically,this component is selected from the group consisting of the compounds ofthe alkali metals -- cesium, rubidium, potassium, sodium, and lithium --and of the alkaline earth metals -- calcium, strontium, barium, andmagnesium. This component exists within the catalytic composite in anoxidation state above that of the elemental metal such as a relativelystable compound such as the oxide or hydroxide, or in combination withone or more of the other components of the composite, or in combinationwith the carrier material such as, for example, in the form of an alkalior alkaline earth metal aluminate. Since, as is explained hereinafter,the composite containing the alkali or alkaline earth component isalways calcined or oxidized in an air atmosphere before use in thedehydrogenation of hydrocarbons, the most likely state this componentexists in during use in the dehydrogenation reaction is thecorresponding metallic oxide such as lithium oxide, potassium oxide,sodium oxide, and the like. Regardless of what precise form in which itexists in the composite, the amount of this component utilized ispreferably selected to provide a nonacidic composite containing about0.1 to about 5 wt. % of the alkali metal or alkaline earth metal, and,more preferably, about 0.25 to about 3.5 wt. %. Best results areobtained when this component is a compound of lithium or potassium. Thefunction of this component is to neutralize any of the acidic materialsuch as halogen which may have been used in the preparation of thepresent catalyst so that the final catalyst is nonacidic.

This alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art toresult in a relatively uniform dispersion of this component throughoutthe carrier material with consequential neutralization of any acidicsites which may be present therein. Typically good results are obtainedwhen it is combined by impregnation, coprecipitation, ion-exchange, andthe like procedures. The preferred procedure, however, involvesimpregnation of the carrier material either before, during, or after itis calcined, or before, during, or after the other metallic ingredientsare added to the carrier material. Best results are ordinarily obtainedwhen this component is added to the carrier material after the platinumgroup and bismuth components because the alkali metal or alkaline earthmetal component acts to neutralize the acidic materials used in thepreferred impregnation procedure for these metallic components. In fact,it is preferred to add the platinum group and bismuth components to thecarrier material, oxidize the resulting composite in a wet air stream ata high temperature (i.e. typically about 600° to 1000° F.), then treatthe resulting oxidized composite with steam or a mixture of air andsteam at a relatively high temperature of about 800° to about 1050° F.in order to remove at least a portion of any residual acidity andthereafter add the cobalt and the alkali metal or alkaline earthcomponents. Typically, the impregnation of the carrier material withthis component is performed by contacting the carrier material with asolution of a suitable decomposable compound or salt of the desiredalkali or alkaline earth metal. Hence, suitable compounds include thealkali metal or alkaline earth metal halides, nitrates, acetates,carbonates, phosphates, and the like compounds. For example, excellentresults are obtained by impregnating the carrier material after theplatinum group and bismuth components have been combined therewith, withan aqueous solution of lithium nitrate or potassium nitrate and cobaltacetate or nitrate.

Regarding the preferred amounts of the metallic components of thesubject catalyst, I have found it to be a beneficial practice to specifythe amounts of these metallic components not only on an absolute basisbut also as a function of the amount of the platinum group component,expressed on an atomic basis. Quantitatively, the amount of the cobaltcomponent is preferably sufficient to provide an atomic ratio of cobaltto platinum group metal of about 0.1:1 to about 66:1, with best resultsobtained at an atomic ratio of about 0.4:1 to about 18:1. Similarly, itis a good practice to specify the amount of the bismuth component sothat the atomic ratio of bismuth to platinum group metal contained inthe composite is about 0.1:1 to about 2:1, with the preferred rangebeing about 0.2:1 to about 1:1. In the same manner, the amount of thealkali or alkaline earth component is ordinarily selected to produce acomposite having an atomic ratio of alkali metal or alkaline earth metalto platinum group metal of about 5:1 to about 100:1 or more, with thepreferred range being about 10:1 to about 75:1.

Another significant parameter for the instant nonacidic catalyst is the"total metals content" which is defined to be the sum of the platinumgroup component, the cobalt component, the bismuth component, and thealkali or alkaline earth component, calculated on an elemental metalbasis. Good results are ordinarily obtained with the subject catalystwhen this parameter is fixed at a value of about 0.2 to about 5 wt. %,with best results ordinarily achieved at a metals loading of about 0.4to about 4 wt. %.

Integrating the above discussion of each of the essential and preferredcomponents of the catalytic composite used in the present invention, itis evident that an especially preferred nonacidic catalytic compositecomprises a combination of a platinum group component, a cobaltcomponent, a bismuth component, and an alkali or alkaline earthcomponent with an alumina carrier material in amounts sufficient toresult in the composite containing from about 0.05 to about 1 wt. %platinum group metal, about 0.1 to about 2.5 wt. % cobalt, about 0.25 toabout 3.5 wt. % alkali metal or alkaline earth metal, and about 0.05 toabout 1 wt. % bismuth.

Regardless of the details of how the components of the catalyst arecombined with the porous carrier material, the resulting multimetalliccomposite generally will be dried at a temperature of about 200° F. toabout 600° F. for a period of from about 2 to about 24 hours or more,and finally calcined or oxidized at a temperature of about 600° F. toabout 1100° F. (preferably about 800° to about 950° F.) in an airatmosphere for a period of about 0.5 to 10 hours, preferably about 1 toabout 5 hours, in order to convert substantially all the metalliccomponents to the corresponding oxide form. When acidic components arepresent in any of the reagents used to effect incorporation of any oneof the components of the subject composite, it is a good practice tosubject the resulting composite to a high temperature treatment withsteam or with a mixture of steam and air, either before, during or afterthis oxidation step in order to remove as much as possible of theundesired acidic component. For example, when the platinum groupcomponent is incorporated by impregnating the carrier material withchloroplatinic acid, it is preferred to subject the resulting compositeto a high temperature treatment with steam or a mixture of steam and airat a temperature of about 600° to 1100° F. in order to remove as much aspossible of the undesired chloride.

The resultant oxidized catalytic composite is preferably subjected to asubstantially water-free reduction step prior to its use in thedehydrogenation of hydrocarbons. This step is designed to selectivelyreduce the platinum group component to the corresponding metal, whilemaintaining the bismuth component in a positive oxidation state, and toinsure a uniform and finely divided dispersion of the metalliccomponents throughout the carrier material. It is a good practice to drythe oxidized catalyst prior to this reduction step by passing a streamof dry air or nitrogen through same at a temperature of about 500° to1100° F. (preferably about 800° to about 950° F.) and at a GHSV of about100 to 800 hr.⁻¹ until the effluent stream contains less than 1000 ppm.of H₂ O and preferably less than 500 ppm. Preferably, a substantiallypure and dry hydrogen stream (i.e. less than 20 vol. ppm. H₂ O) is usedas the reducing agent in this reduction step. The reducing agent iscontacted with the oxidized catalyst at conditions including atemperature of about 600° F. to about 1200° F. (preferably about 800° toabout 1000° F.), a GHSV of about 300 to 1000 hr.⁻¹, and a period of timeof about 0.5 to 10 hours effective to reduce substantially all of theplatinum group component to the elemental metallic state, whilemaintaining the bismuth component in an oxidation state above that ofthe elemental metal. This reduction treatment may be performed in situas part of a start-up sequence if precautions are taken to predry theplant to a substantially water-free state and if a substantiallywater-free hydrogen stream is used.

Although maintaining the subject catalyst in a substantially sulfur-freestate is an especially preferred mode of operation for the presentinvention (as explained in the teachings of my prior application Ser.No. 602,935), the resulting selectively reduced catalytic composite mayin some circumstances be beneficially subjected to a presulfidingoperation designed to incorporate in the catalytic composite from about0.01 to about 0.5 wt. % sulfur, calculated on an elemental basis.Preferably, this presulfiding treatment takes place in the presence ofhydrogen and a suitable sulfur-containing sulfiding reagent such ashydrogen sulfide, lower molecular weight mercaptans, organic sulfides,etc. Typically, this procedure comprises treating the selectivelyreduced catalyst with a sulfiding reagent such as a mixture of hydrogenand hydrogen sulfide having about 10 moles of hydrogen per mole ofhydrogen sulfide at conditions sufficient to effect the desiredincorporation of sulfur, generally including a temperature ranging fromabout 50° F. up to about 1100° F. or more. It is generally a goodpractice to perform this presulfiding step under substantiallywater-free conditions. Although not preferred, it is within the scope ofthe present invention to maintain or achieve the sulfided state of theinstant catalyst during use in the conversion of hydrocarbons bycontinuously or periodically adding a decomposable sulfur-containingcompound, such as the sulfiding reagents previously mentioned, to thereactor containing the catalyst in an amount sufficient to provide about1 to 500 wt. ppm., preferably 1 to 20 wt. ppm. of sulfur based onhydrocarbon charge.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the multimetallic catalytic compositedescribed above in a dehydrogenation zone maintained at dehydrogenationconditions. This contacting may be accomplished by using the catalyst ina fixed bed system, a moving bed system, a fluidized bed system, or in abatch type operation; however, in view of the danger of attrition lossesof the valuable catalyst and of well-known operational advantages, it ispreferred to use a fixed bed system. In this system, the hydrocarbonfeed stream is preheated by any suitable heating means to the desiredreaction temperature and then passed into a dehydrogenation zonecontaining a fixed bed of the catalyst previously characterized. It is,of course, understood that the dehydrogenation zone may be one or moreseparate reactors with suitable heating means therebetween to insurethat the desired conversion temperature is maintained at the entrance toeach reactor. It is also to be noted that the reactants may be contactedwith the catalyst bed in either upward, downward, or radial flow fashionwith the latter being preferred. In addition, it is to be noted that thereactants may be in the liquid phase, a mixed liquid-vapor phase, or avapor phase when they contact the catalyst, with best results obtainedin the vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized, either individually or in admixture withhydrogen or each other, such as steam, methane, ethane, carbon dioxide,and the like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehydrogenatable hydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recycledhydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. As is explained in my priorapplication Ser. No. 602,935, a highly preferred mode of operation ofthe instant dehydrogenation method is in a substantially water-freeenvironment; however, when utilizing hydrogen in the instant method,improved selectivity results are obtained under certain limitedcircumstances, if water or a water-producing substance (such as analcohol, ketone, ether, aldehyde, or the like oxygen-containingdecomposable organic compound) is added to the dehydrogenation zone inan amount calculated on the basis of equivalent water, corresponding toabout 1 to about 5,000 wt. ppm. of the hydrocarbon charge stock, withabout 1 to 1,000 wt. ppm. of water giving best results. This wateraddition feature may be used on a continuous or intermittent basis toregulate the activity and selectivity of the instant catalyst.

Regarding the conditions utilized in the method of the presentinvention, these are generally selected from the dehydrogenationconditions well known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° to about 1200° F. with a value being selected fromthe lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the higherportion of this range for the more difficultly dehydrogenatedhydrocarbons such as propane, butane, and the like hydrocarbons. Forexample, for the dehydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarily obtained at a temperature of about 800° to about950° F. The pressure utilized is ordinarily selected at a value which isas low as possible consistent with the maintenance of catalyst stabilityand is usually about 0.1 to about 10 atmospheres with best resultsordinarily obtained in the range of about 0.5 to about 3 atmospheres. Inaddition, a liquid hourly space velocity (calculated on the basis of thevolume amount, as a liquid, of hydrocarbon charged to thedehydrogenation zone per hour divided by the volume of the catalyst bedutilized) is selected from the range of about 1 to about 40 hr.⁻¹, withbest results for the dehydrogenation of long chain normal paraffinstypically obtained at a relatively high space velocity of about 25 to 35hr.⁻¹.

Regardless of the details concerning the operation of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is allowed to separate from ahydrocarbon-rich liquid phase. In general, it is usually desired torecover the unreacted dehydrogenatable hydrocarbon from thishydrocarbon-rich liquid phase in order to make the dehydrogenationprocess economically attractive. This recovery operation can beaccomplished in any suitable manner known to the art such as by passingthe hydrocarbon-rich liquid phase through a bed of suitable adsorbentmaterial which has the capability to selectively retain thedehydrogenated hydrocarbons contained therein or by contacting same witha solvent having a high selectivity for the dehydrogenated hydrocarbon,or by a suitable fractionation scheme where feasible. In the case wherethe dehydrogenated hydrocarbon is a mono-olefin, suitable adsorbentshaving this capability are activated silica gel, activated carbon,activated alumina, various types of specially prepared zeoliticcrystalline aluminosilicates, molecular sieves, and the like adsorbents.In another typical case, the dehydrogenated hydrocarbons can beseparated from the unconverted dehydrogenatable hydrocarbons byutilizing the inherent capability of the dehydrogenated hydrocarbons toeasily enter into several well-known chemical reactions such asalkylation, oligomerization, halogenation, sulfonation, hydration,oxidation, and the like reactions. Irrespective of how thedehydrogenated hydrocarbons are separated from the unreactedhydrocarbons, a stream containing the unreacted dehydrogenatablehydrocarbons will typically be recovered from this hydrocarbonseparation step and recycled to the dehydrogenation step. Likewise, thehydrogen phase present in the hydrogen-separating zone will be withdrawntherefrom, a portion of it vented from the system in order to remove thenet hydrogen make, and the remaining portion is typically recycledthrough suitable compressing means to the dehydrogenation step in orderto provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof unconverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thedehydrogenation method and nonacidic multimetallic catalytic compositeof the present invention. These examples of specific embodiments of thepresent invention are intended to be illustrative rather thanrestrictive.

These examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, heating means,cooling means, pumping means, compressing means, and the likeconventional equipment. In this plant, the feed stream containing thedehydrogenatable hydrocarbon is combined with a hydrogen-containingrecycle gas stream containing water in an amount corresponding to about100 wt. ppm. of the hydrocarbon feed and the resultant mixture heated tothe desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the instant multimetallic catalystwhich is maintained as a fixed bed of catalyst particles in the reactor.The pressures reported herein are recorded at the outlet from thereactor. An effluent stream is withdrawn from the reactor, cooled, andpassed into the hydrogen-separating zone wherein a hydrogen-containinggas phase separates from a hydrocarbon-rich liquid phase containingdehydrogenated hydrocarbons, unconverted dehydrogenatable hydrocarbons,and a minor amount of side products of the dehydrogenation reaction. Aportion of the hydrogen-containing gas phase is recovered as excessrecycle gas with the remaining portion being continuously recycled,after water addition as needed, through suitable compressing means tothe heating zone as described above. The hydrocarbon-rich liquid phasefrom the separating zone is withdrawn therefrom and subjected toanalysis to determine conversion and selectivity for the desireddehydrogenated hydrocarbon as will be indicated in the Examples.Conversion numbers of the dehydrogenatable hydrocarbon reported hereinare all calculated on the basis of disappearance of the dehydrogenatablehydrocarbon and are expressed in mole percent. Similarly, selectivitynumbers are reported on the basis of moles of desired hydrocarbonproduced per 100 moles of dehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared accordingto the following preferred method with suitable modification instoichiometry to achieve the compositions reported in each example.First, an alumina carrier material comprising 1/16 inch spheres havingan apparent bulk density of about 0.3 g/cc is prepared by: forming analumina hydroxyl chloride sol by dissolving substantially pure aluminumpellets in a hydrochloric acid solution, adding hexamethylenetetramineto the resulting alumina sol, gelling the resulting solution by droppingit into an oil bath to form spherical particles of an alumina hydrogel,aging, and washing the resulting particles with an ammoniacal solutionand finally drying, calcining, and steaming the aged and washedparticles to form spherical particles of gamma-alumina containingsubstantially less than 0.1 wt. % combined chloride. Additional detailsas to this method of preparing this alumina carrier material are givenin the teachings of U.S. Pat. No. 2,620,314.

The resulting gamma-alumina particles are then contacted in a firstimpregnation step at suitable impregnation conditions with a firstaqueous impregnation solution containing chloroplatinic acid, nitricacid and bismuth nitrate in amounts sufficient to yield a finalmultimetallic catalytic composite containing a uniform dispersion of thehereinafter specified amounts of platinum and bismuth. The nitric acidis utilized in an amount of about 5 wt. % of the alumina particles. Inorder to ensure a uniform dispersion of the metallic components in thecarrier material, the impregnation solution is maintained in contactwith the carrier material particles for about 1/2 hour at a temperatureof about 70° F. with constant agitation. The impregnated spheres arethen dried at a temperature of about 225° F. for about an hour andthereafter calcined or oxidized in an air atmosphere containing about 5to 25 vol. % H₂ O at a temperature of about 500° F. to about 1000° F.(preferably about 800° to 950° F.) for about 2 to 10 hours effective toconvert all of the metallic components to the corresponding oxide forms.In general, it is a good practice to thereafter treat the resultingoxidized particles with an air stream containing about 10 to about 30%steam at a temperature of about 800° F. to about 1000° F. for anadditional period of about 1 to about 5 hours in order to reduce anyresidual combined chloride contained in the catalyst to a value of lessthan 0.5 wt. % and preferably less than 0.2 wt. %.

The cobalt component is thereafter added to this oxidized andsteam-stripped catalyst in a second impregnation step. In the casesshown in the examples where the catalyst utilized contains an alkali oralkaline earth component, this component is also added to the oxidizedand steam-treated multimetallic catalyst in this second impregnationstep. This second impregnation step involves contacting the oxidized andsteamed multimetallic catalyst with an aqueous acidic solution of asuitable soluble and decomposable salt of cobalt and of the alkali oralkaline earth component (when it is to be added) under conditionsselected to result in a uniform dispersion of these components in thecarrier material. For the catalysts utilized in the present examples,the salts are cobalt nitrate or acetate and either lithium nitrate orpotassium nitrate. The amounts of the salts of cobalt and of the alkalimetal utilized are chosen to result in a final catalyst containing therequired amount of cobalt and having the desired nonacidiccharacteristics. The resulting cobalt and alkali or alkalineearth-impregnated particles are then preferably dried and oxidized in anair atmosphere in much the same manner as is described above followingthe first impregnation step. In some cases, it is possible to combineboth of these impregnation steps into a single step, therebysignificantly reducing the time and complexity of the catalystmanufacturing procedure.

The resulting oxidized catalyst is thereafter subjected to a drying stepwhich involves contacting the oxidized particles with a dry air streamat a temperature of about 930° F., a GHSV of 300 hr.⁻¹ for a period ofabout 10 hours. The dried catalyst is then purged with a dry nitrogenstream and thereafter selectively reduced by contacting with a dryhydrogen stream at conditions including a temperature of about 870° F.,atmospheric pressure and a gas hourly space velocity of about 500 hr.⁻¹,for a period of about 1 to 10 hours effective to at least reducesubstantially all of the platinum group component to the correspondingelemental metal, while maintaining the alkali or alkaline earth andbismuth components in a positive oxidation state.

EXAMPLE I

The reactor is loaded with 100 cc of a catalyst containing, on anelemental basis, 0.3 wt. % platinum, 1.0 wt. % cobalt and 0.2 wt. %bismuth, and less than 0.15 wt. % chloride. This corresponds to anatomic ratio of bismuth to platinum of 0.62:1 and of cobalt to platinumof 11:1. The feed stream utilized is commercial grade isobutanecontaining 99.7 wt. % isobutane and 0.3 wt. % normal butane. The feedstream is contacted with the catalyst at a temperature of 1020° F., apressure of 10 psig., a liquid hourly space velocity of 4.0 hr.⁻¹, and arecycle gas to hydrocarbon mole ratio of 3:1. The dehydrogenation plantis lined-out at these conditions and a 20 hour test period commenced.The hydrocarbon product stream from the plant is continuously analyzedby GLC (gas liquid chromatography) and a high conversion of isobutane isobserved with a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt. % platinum, 0.5wt. % cobalt, 0.1 wt. % bismuth, 0.6 wt. % lithium, and 0.15 wt. %combined chloride. These amounts correspond to the following atomicratios: (1) Bi/Pt of 0.25:1, (2) Co/Pt of 4.41:1, and (3) Li/Pt of 45:1.The feed stream is commercial grade normal dodecane. The dehydrogenationreactor is operated at a temperature of 850° F., a pressure of 10 psig.,a liquid hourly space velocity of 32 hr.⁻¹, and a recycle gas tohydrocarbon mole ratio of 5:1. After a line-out period, a 20 hour testperiod is performed during which the average conversion of the normaldodecane is maintained at a high level with a selectivity for normaldodecane of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 830°F., a pressure of 20 psig., a liquid hourly space velocity of 32 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 4:1. After a line-outperiod, a 20 hour test shows an average conversion of about 12%, and aselectivity for normal tetradecane of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.3 wt. % platinum, 1.0wt. % cobalt, 0.15 wt. % bismuth, and 0.6 wt. % lithium, with combinedchloride being less than 0.2 wt. %. The pertinent atomic ratios are: (1)Bi/Pt of 0.47:1, (2) Co/Pt of 11:1, and (3) Li/Pt of 56:1. The feedstream is substantially pure cyclohexane. The conditions utilized are atemperature of 900° F., a pressure of 100 psig., a liquid hourly spacevelocity of 3.0 hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of4:1. After a line-out period, a 20 hour test is performed with almostquantitative conversion of cyclohexane to benzene and hydrogen.

EXAMPLE V

The catalyst contains, on an elemental basis, 0.6 wt. % platinum, 1.0wt. % cobalt, 0.3 wt. % bismuth, 1.5 wt. % potassium, and less than 0.2wt. % combined chloride. The governing atomic ratios are: (1) Bi/Pt of0.47:1, (2) Co/Pt of 5.5:1 and (3) K/Pt of 12.5:1. The feed stream iscommercial grade ethylbenzene. The conditions utilized are a pressure of15 psig., a liquid hourly space velocity of 32 hr.⁻¹, a temperature of1010° F., and a recycle gas to hydrocarbon mole ratio of 3:1. During a20 hour test period, 85% or more of equilibrium conversion of theethylbenzene is observed. The selectivity for styrene is about 90%.

It is intended to cover by the following claims, all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A nonacidic catalytic composite comprising aporous carrier material containing, on an elemental basis, about 0.01 toabout 2 wt. % platinum group metal, about 0.05 to about 5 wt. % cobalt,and about 0.01 to about 5 wt. % bismuth, wherein the platinum groupmetal, catalytically available cobalt and bismuth are uniformlydispersed throughout the porous carrier material; wherein substantiallyall of the platinum group metal is present in the elemental metallicstate; wherein substantially all of the bismuth is present in anoxidation state above that of the elemental metal; and whereinsubstantially all of the catalytically available cobalt is present inthe elemental metallic state or in a state which is reducible to theelemental metallic state under dehydrogenation conditions or in amixture of these states.
 2. A catalytic composite as defined in claim 1wherein the platinum group metal is platinum.
 3. A catalytic compositeas defined in claim 1 wherein the platinum group metal is iridium.
 4. Acatalytic composite as defined in claim 1 wherein the platinum groupmetal is rhodium.
 5. A catalytic composite as defined in claim 1 whereinthe platinum group metal is palladium.
 6. A catalytic composite asdefined in claim 1 wherein the catalytic composite is in a sulfur-freestate.
 7. A catalytic composite as defined in claim 1 wherein the porouscarrier material is a refractory inorganic oxide.
 8. A catalyticcomposite as defined in claim 7 wherein the refractory inorganic oxideis alumina.
 9. A catalytic composite as defined in claim 1 wherein thecomposite contains on an elemental basis, about 0.05 to about 1 wt. %platinum group metal, about 0.1 to about 2.5 wt. % cobalt and about 0.05to about 1 wt. % bismuth.
 10. A catalytic composite as defined in claim1 wherein the metals content of the catalytic composite is adjusted sothat the atomic ratio of bismuth to platinum group metal is about 0.1:1to about 2:1 and the atomic ratio of cobalt to platinum group metal isabout 0.1:1 to about 66:1.
 11. A catalytic composite as defined in claim1 wherein substantially all of the bismuth is present in the catalyticcomposite as bismuth oxide or bismuth aluminate.
 12. A catalyticcomposite as defined in claim 1 wherein substantially all of thecatalytically available cobalt contained in the composite is present inthe elemental metallic state.
 13. A nonacidic catalytic compositecomprising a porous carrier material containing, on an elemental basis,about 0.01 to about 2 wt. % platinum group metal, about 0.05 to about 5wt. % cobalt, about 0.1 to about 5 wt. % alkali metal or alkaline earthmetal, and about 0.01 to about 5 wt. % bismuth; wherein the platinumgroup metal, catalytically available cobalt, bismuth and alkali metal oralkaline earth metal are uniformly dispersed throughout the porouscarrier material; wherein substantially all of the platinum group metalis present in the elemental metallic state; wherein substantially all ofthe bismuth is present in an oxidation state above that of the elementalmetal; wherein substantially all of the catalytically available cobaltis present in the elemental metallic state or in a state which isreducible to the elemental metallic state under dehydrogenationconditions or in a mixture of these states; and wherein substantiallyall of the alkali metal or alkaline earth metal is present in anoxidation state above that of the elemental metal.
 14. A nonacidiccatalytic composite as defined in claim 13 wherein the porous carriermaterial is a refractory inorganic oxide.
 15. A nonacidic catalyticcomposite as defined in claim 14 wherein the refractory inorganic oxideis alumina.
 16. A nonacidic catalytic composite as defined in claim 13wherein the alkali metal or alkaline earth metal is potassium.
 17. Anonacidic catalytic composite as defined in claim 13 wherein the alkalimetal or alkaline earth metal is lithium.
 18. A nonacidic catalyticcomposite as defined in claim 13 wherein the catalytic composite is in asulfur-free state.
 19. A nonacidic catalytic composite as defined inclaim 13 wherein the composite contains, on an elemental basis, about0.05 to about 1 wt. % platinum group metal, about 0.1 to about 2.5 wt. %cobalt, about 0.05 to about 1 wt. % bismuth and about 0.25 to about 3.5wt. % alkali metal or alkaline earth metal.
 20. A nonacidic catalyticcomposite as defined in claim 13 wherein the metals contents thereof isadjusted so that the atomic ratio of bismuth to platinum group metal isabout 0.1:1 to about 2:1, the atomic ratio of alkali metal or alkalineearth metal to platinum group metal is about 5:1 to about 100:1 and theatomic ratio of cobalt to platinum group metal is about 0.1:1 to 66:1.